In recent years, hybrid vehicles using both of a motor and an engine for driving wheels have been of interest as environment-friendly vehicles. Such hybrid vehicles include those under study that are mounted with a plurality of batteries.
Japanese Patent Laying-Open No. 2003-209969 discloses a hybrid vehicle mounted with a plurality of batteries. A power control system for an electric traction motor in the vehicle includes at least one inverter for providing conditioned electrical power to the electric traction motor, and a plurality of power stages for providing DC power to said at least one inverter, where each stage includes a battery and a boost/buck DC-DC converter, and said power stages are wired in parallel. The power stages are controlled to maintain an output voltage to said at least one inverter.
A hybrid vehicle chargeable from an external source is also under study. Such a vehicle may be charged at home for example, so that the frequency of replenishment with fuel at a gas station decreases, which is convenient for the driver. Further, more cost-effective midnight power for example may be used, so that an advantage in terms of the cost is achieved.
The charging efficiency in home charging for example, however could be deteriorated due to generation of heat and the like. In order to improve the overall energy efficiency, it is necessary to keep small the loss in charging from an external source.